This invention relates to a manufacturing method for pipes having branched pipes, such as manifolds.
Pipe members having branch pipes on the periphery thereof are often used to connect other pipes or devices to each other.
A known method for manufacturing a pipe with branch pipes of this type comprises the step of opening holes on the peripheral surface of a pipe member, and connecting other pipe members at their ends over the holes by welding. But this method needs much labour for welding, especially when the number of branch pipes is larger as in the case of a manifold, and moreover, the strength of the pipe member is susceptible to deterioration owing to the heat during the welding process.
In order to overcome such defects, a bulging process has been employed for forming a pipe having branch pipes in recent years.
The bulging process comprises the steps of inserting a pipe member into a bulge mold which has recesses or spaces for forming bulges, pressurizing fluid (such as water) into the pipe member to deform and bulge the material of the pipe member into spaces in the bulge mold, forming projections from the peripheral surface of the pipe material, and forming the branch pipes either by cutting the tip ends of the projections or opening holes thereon.
However, the aforementioned bulging process is detrimental in that when the length or diameter of a branch pipe is large, the thickness thereof becomes insufficient since the bulged portioin or the projection has been made with material gathered around the location. The strength of the pipe therefore is not sufficient.
Further, although one or two projections may be formed with a sufficient thickness even if they are formed with the material gathered from the surrounding areas, when three or more projections are to be formed simultaneously, the material required for the middle projections is prevented from being gathered by two adjacent branch pipes. The thickness of the projection at the middle is inevitably insufficient and presents a problem in the manufacturing process.